Positive electrode for all-solid rechargeable battery and all-solid rechargeable battery

Abstract

The present invention relates to a positive electrode for an all-solid rechargeable battery and an all-solid rechargeable battery comprising same, the positive electrode comprising: a current collector; a carbon coating layer positioned on the current collector; a polydopamine coating layer positioned on the carbon coating layer; and a positive electrode active material layer positioned on the polydopamine coating layer and containing a positive electrode active material and a sulfide-based solid electrolyte.

Description

Cathode for all-solid-state secondary batteries and all-solid-state secondary batteries

[0001] The present invention relates to a positive electrode for an all-solid-state secondary battery and an all-solid-state secondary battery including the same.

[0002] Lithium secondary batteries, which boast high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] Commercially available lithium secondary batteries use electrolytes containing flammable organic solvents, posing safety concerns, such as explosions or fires in the event of collisions or penetrations. Therefore, semi-solid or all-solid-state batteries that avoid the use of electrolytes are being proposed. All-solid-state secondary batteries are composed entirely of solid materials, specifically those that utilize solid electrolytes. These all-solid-state secondary batteries are safe, eliminating the risk of electrolyte leakage and explosion, and offer the advantage of being easy to manufacture in thin forms.

[0004] All-solid-state secondary battery cathodes typically contain a cathode active material and a solid electrolyte. Sulfide-based solid electrolytes, which exhibit high ionic conductivity and superior mechanical properties, are commonly used. However, the sulfide-based solid electrolytes present in the cathode have the disadvantage of reacting with conductive materials within the battery, decomposing and causing deterioration. To address this issue, methods for coating the surface of the conductive material used in all-solid-state secondary battery cathodes with inorganic or organic materials have been studied.

[0005] By suppressing the interfacial side reaction between the conductive material and the sulfide-based solid electrolyte in the positive electrode for an all-solid-state secondary battery, deterioration of the sulfide-based solid electrolyte is prevented, and the adhesion between the current collecting substrate and the positive electrode active material layer is increased and the contact area is maximized to lower the interfacial electronic resistance, thereby improving the performance of the all-solid-state secondary battery.

[0006] In one embodiment, a positive electrode for an all-solid-state secondary battery is provided, including a current collector, a carbon coating layer positioned on the current collector, a polydopamine coating layer positioned on the carbon coating layer, and a positive electrode active material layer positioned on the polydopamine coating layer and containing a positive electrode active material and a sulfide-based solid electrolyte.

[0007] In another embodiment, an all-solid-state secondary battery is provided, comprising the positive electrode, the negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0008] In a positive electrode for an all-solid-state secondary battery according to an embodiment, side reactions of a sulfide-based solid electrolyte are suppressed, deterioration is prevented, and interfacial electronic resistance is reduced, thereby improving the electrochemical characteristics of the all-solid-state secondary battery.

[0009] Figures 1 and 2 are cross-sectional views schematically showing an all-solid-state secondary battery structure according to one embodiment.

[0010] Below, specific implementation examples are described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the implementation examples described herein.

[0011] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0012] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0013] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0015] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0016] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size can mean the diameter (D50) of particles in a particle size distribution that have a cumulative volume of 50% by volume. In addition, unless otherwise defined, the average particle size can be obtained by randomly measuring the sizes (diameters or major axis lengths) of about 20 particles in a scanning electron microscope image to obtain a particle size distribution, and taking the diameter (D50) of particles in the particle size distribution that have a cumulative volume of 50% by volume as the average particle size.

[0017] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0018] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0019] anode

[0020] In one embodiment, a positive electrode for an all-solid-state secondary battery is provided, including a current collector, a carbon coating layer positioned on the current collector, a polydopamine coating layer positioned on the carbon coating layer, and a positive electrode active material layer positioned on the polydopamine coating layer and containing a positive electrode active material and a sulfide-based solid electrolyte.

[0021] The above carbon coating layer may be a conductive particle layer including conductive particles, and serves to increase the interfacial area between the current collector and the positive electrode active material layer, thereby improving the adhesive strength and lowering the electronic resistance at the interface. However, such a carbon coating layer causes a side reaction at the interface with the sulfide-based solid electrolyte particles present in the positive electrode active material layer during battery operation, which causes a problem in that the sulfide-based solid electrolyte deteriorates. In one embodiment, by introducing a polydopamine coating layer on the carbon coating layer, the side reaction between the conductive particles of the carbon coating layer and the sulfide-based solid electrolyte of the positive electrode active material layer is suppressed, thereby preventing the deterioration of the sulfide-based solid electrolyte, and further successfully maximizing the contact area between the positive electrode active material layer and the polydopamine coating layer and increasing the adhesive strength, thereby further lowering the interfacial electronic resistance.

[0022] The above-described current collector, carbon coating layer, and polydopamine coating layer can be considered a type of positive electrode substrate, and can be said to be a positive electrode substrate capable of preventing deterioration of a sulfide-based solid electrolyte. Such a positive electrode substrate has high adhesion to the positive electrode active material layer, low interfacial resistance, and can effectively suppress the problem of deterioration of the sulfide-based solid electrolyte during battery operation.

[0023] The current collector may include, but is not limited to, aluminum, nickel, stainless steel, or a combination thereof. The thickness of the current collector is not particularly limited and may be, for example, 1 μm to 30 μm, 1 μm to 20 μm, or 1 μm to 10 μm.

[0024] The thickness of the carbon coating layer may be 1 nm to 50 nm, for example, 1 nm to 30 nm, 1 nm to 20 nm, or 5 nm to 20 nm, in which case the adhesion between the positive electrode substrate and the positive electrode active material layer may be increased and the electrochemical characteristics of the positive electrode may be improved.

[0025] The carbon coating layer includes a carbon material, and may include, for example, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, or a combination thereof.

[0026] The above polydopamine coating layer is a coating layer containing polydopamine, and polydopamine can mean a polymer made of dopamine oxide and is interpreted as a concept that also includes derivatives of polydopamine, and is applied without limitation to any commercially available polydopamine. For example, the above polydopamine is dopamine hydrochloride (C8H 11 It may contain or be derived from NO2·HCl) and its molecular weight may be approximately 100 g / mol to 300 g / mol.

[0027] The polydopamine coating layer may cover the carbon coating layer in a continuous film form. The polydopamine coating layer is formed to have a thickness of several to several tens of nanometers, and can effectively prevent deterioration of the sulfide-based solid electrolyte without adversely affecting the battery, improve the adhesion of the positive electrode, and reduce the interfacial resistance. The thickness of the polydopamine coating layer may be 1 nm to 20 nm, for example, 1 nm to 15 nm, 1 nm to 10 nm, 1 nm to 8 nm, or 1 nm to 5 nm. The thickness of the polydopamine coating layer may be, for example, 5 nm or less. By forming it to such a thin thickness, the solid electrolyte can be effectively protected while reducing the interfacial resistance. The polydopamine coating layer not only prevents side reactions between the sulfide-based solid electrolyte and the conductive material, but also has high adhesive strength, thereby improving the adhesion between the substrate and the positive electrode active material layer, and reducing the interfacial electrical resistance.

[0028] Below, the positive electrode active material layer is described.

[0029] The above-mentioned positive electrode active material layer includes a sulfide-based solid electrolyte. The above-mentioned sulfide-based solid electrolyte particles include, for example, Li2S-P2S5, Li2S-P2S5--LiX (wherein X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z. m S n (m, n are integers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or a combination thereof.

[0030] Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10, or 50:50 to 80:20, and optionally heat-treating them. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, the ionic conductivity can be further improved by further including other components such as SiS2, GeS2, and B2S3.

[0031] Methods for mixing sulfur-containing raw materials for producing sulfide-based solid electrolytes include mechanical milling or the solution method. Mechanical milling involves placing raw materials in a ball mill reactor and vigorously stirring them to finely atomize and mix them. Using the solution method, the raw materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, heat treatment after mixing can solidify the crystals of the solid electrolyte and improve ionic conductivity. For example, a sulfide-based solid electrolyte can be produced by mixing sulfur-containing raw materials and heat-treating them twice or more, resulting in a sulfide-based solid electrolyte with high ionic conductivity and robustness.

[0032] According to one embodiment, a sulfide-based solid electrolyte can be manufactured through, for example, a first heat treatment in which sulfur-containing raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the first heat treatment result is mixed and calcined at 350°C to 800°C. The first heat treatment and the second heat treatment can each be performed in an inert gas or nitrogen atmosphere. The first heat treatment can be performed for 1 to 10 hours, and the second heat treatment can be performed for 5 to 20 hours. The first heat treatment can have the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and robustness can be obtained, and such a solid electrolyte can be said to be suitable for mass production. The temperature of the first heat treatment may be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of the second heat treatment may be, for example, 380°C to 700°C, or 400°C to 600°C.

[0033] For example, the sulfide-based solid electrolyte may include an argyrodite-type sulfide. The argyrodite-type sulfide may be, for example, Li aM b P c S d A e (wherein a, b, c, d, and e are all 0 or more and 12 or less, M is Ge, Sn, Si, or a combination thereof, and A is F, Cl, Br, or I) and can be expressed by the chemical formula, and a specific example is Li 7-x PS 6-x A x (x is 0.2 or more and 1.8 or less, and A is F, Cl, Br, or I) can be expressed by the chemical formula. The above argyrodite-type sulfide is specifically Li3PS4, Li7P3S 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 It could be the back.

[0034] Sulfide-based solid electrolytes containing these argyrodite-type sulfides have an ionic conductivity of 10 that of typical liquid electrolytes at room temperature. -4 10 inland -2 It has a high ionic conductivity approaching the S / cm range, can form a close bond between a positive electrode active material and a solid electrolyte without causing a decrease in ionic conductivity, and can further form a close interface between an electrode layer and a solid electrolyte layer. An all-solid-state secondary battery including this can have improved battery performance, such as rate characteristics, Coulombic efficiency, and cycle life characteristics.

[0035] The argyrodite-type sulfide-based solid electrolyte may include, for example, a compound represented by the chemical formula 21 below.

[0036] [Chemical Formula 21]

[0037] (Li a M 1 b M 2 c )(P d M 3e )(S f M 4 g )X h

[0038] In the above chemical formula 21, 4≤a≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, and 0≤b<0.5, and M 2 is Na, K, or a combination thereof, 0≤c<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d<4, 0≤e<1 이고, M 4 is N,O,SO n , or a combination thereof, and 1.5≤n≤5, 3≤f≤12, 0≤g<2, and X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0039] For example, in chemical formula 21, a halide element (X) may be included as an essential element, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 21에 M 1 Elements may be required, in which case 0 <b<0.5로 표시될 수 있다. 화학식 21에서 M 3 can be understood as an element substituted in place of P and 0 <e<1일 수 있다. 화학식 21에서 M 4 is substituted in the S position, for example, 0 <g<2일 수 있으며 S의 비율인 f는 예를 들어 3≤f≤7일 수 있다. M 4 Go SO n If SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0040] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0041] As a specific example, argyrodite-type sulfide-based solid electrolyte particles include Li3PS4 and Li7P3S.11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60 (SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 , or combinations thereof, but are not limited thereto.

[0042] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, and optionally, lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing an argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350°C to 800°C.

[0043] The above sulfide-based solid electrolyte is in the form of particles, and the average particle diameter (D50) of the particles may be 5.0 ㎛ or less, for example, 0.1 ㎛ to 5.0 ㎛, 0.5 ㎛ to 5.0 ㎛, 0.5 ㎛ to 4.0 ㎛, 0.5 ㎛ to 3.0 ㎛, 0.5 ㎛ to 2.0 ㎛, or 0.5 ㎛ to 1.0 ㎛. The solid electrolyte may be small particles having a size of 0.1 ㎛ to 1.9 ㎛, large particles having a size of 2.0 ㎛ to 5.0 ㎛, or a mixture thereof. The average particle diameter of the sulfide-based solid electrolyte particles may be measured by an electron microscope image, and for example, a particle size distribution may be obtained by measuring the size (diameter or major axis length) of about 20 particles in a scanning electron microscope image, and D50 may be calculated therefrom.

[0044] With respect to 100 wt% of the above-mentioned positive electrode active material layer, the sulfide-based solid electrolyte may be included in an amount of 0.1 wt% to 35 wt%, for example, 1 wt% to 35 wt%, 5 wt% to 30 wt%, 8 wt% to 25 wt%, or 10 wt% to 20 wt%.

[0045] The above-described positive electrode active material layer comprises a positive electrode active material. The positive electrode active material may be applied without limitation as long as it is generally used in all-solid-state secondary batteries. For example, the positive electrode active material may be a compound capable of reversible lithium intercalation and deintercalation, and may include a compound represented by any one of the following chemical formulas.

[0046] Li a A 1-b X b D2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5);

[0047] Li a A 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0048] Li a E 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0049] Li a E 2-b X b O 4-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0050] Li a Ni 1-b-c Co b X c D α (0.90 ≤ a ≤1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 <α ≤ 2);

[0051] Li a Ni 1-b-c Co b X c O 2-α T α(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0052] Li a Ni 1-b-c Co b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0053] Li a Ni 1-b-c Mr b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2);

[0054] Li a Ni 1-b-c Mr b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0055] Li a Ni 1-b-c Mr b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0056] Li a Ni b HAVE BEEN c G d O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1);

[0057] Li a Ni b Co c Mr d G eO2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤0.5, 0.001 ≤ e ≤ 0.1);

[0058] Li a NiG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0059] Li a CoG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0060] Li a Mn 1-b G b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0061] Li a Mn2G b O4(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0062] Li a Mn 1-g G g PO4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5);

[0063] QO2; QS2; LiQS2;

[0064] V2O5; LiV2O5;

[0065] LiZO2;

[0066] LiNiVO4;

[0067] Li (3-f) J2(PO4)3(0 ≤ f ≤ 2);

[0068] Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2);

[0069] Li a FePO4(0.90 ≤ a ≤ 1.8).

[0070] In the above chemical formulas, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0071] The above-mentioned positive electrode active material may be, for example, lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt oxide (NC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium nickel manganese oxide (NM), lithium manganese oxide (LMO), or lithium iron phosphate (LFP).

[0072] The positive electrode active material may include, for example, a lithium nickel-based oxide represented by the following chemical formula 1, a lithium cobalt-based oxide represented by the following chemical formula 2, a lithium iron phosphate-based compound represented by the following chemical formula 3, a cobalt-free lithium nickel-manganese-based oxide represented by the following chemical formula 4, or a combination thereof.

[0073] [Chemical Formula 1]

[0074] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0075] In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0076] In the above chemical formula 1, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0077] [Chemical Formula 2]

[0078] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0079] In the above chemical formula 2, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, and M 3 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0080] [Chemical Formula 3]

[0081] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0082] In the above chemical formula 3, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, and M 4 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0083] [Chemical Formula 4]

[0084] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0085] In the above chemical formula 4, 0.9≤a2≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b4≤0.1이고 M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0086] The average particle diameter (D50) of the positive electrode active material may be 1 μm to 25 μm, for example, 3 μm to 25 μm, 1 μm to 20 μm, 1 μm to 18 μm, 3 μm to 15 μm, or 5 μm to 15 μm. For example, the positive electrode active material may include small particles having an average particle diameter (D50) of 1 μm to 9 μm and large particles having an average particle diameter (D50) of 10 μm to 25 μm. A positive electrode active material having such a particle diameter range can be harmoniously mixed with other components within a positive electrode active material layer and can realize high capacity and high energy density. Here, the average particle diameter may be obtained by selecting 20 or so random particles from a scanning electron microscope image of the positive electrode active material, measuring their particle diameters (diameter, major axis, or major axis length), obtaining a particle size distribution, and then taking the diameter (D50) of particles having a cumulative volume of 50% by volume from the particle size distribution as the average particle diameter.

[0087] The above-mentioned positive electrode active material may be in the form of a secondary particle formed by agglomeration of a plurality of primary particles, or may be in the form of a single particle. In addition, the above-mentioned positive electrode active material may be spherical or nearly spherical in shape, or may be polyhedral or irregular in shape.

[0088] Meanwhile, the positive electrode active material may include a buffer layer on the particle surface. The buffer layer may be expressed as a coating layer, a protective layer, etc., and may play a role in lowering the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte particles. For example, the buffer layer may include a lithium-metal-oxide, wherein the metal may be one or more elements selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr. The lithium-metal-oxide is excellent in lowering the interfacial resistance between the positive electrode active material and the solid electrolyte particles while improving the performance of the positive electrode active material by facilitating the movement of lithium ions and electron conduction.

[0089] The positive electrode active material may be included in an amount of 55 wt% to 99 wt% based on 100 wt% of the positive electrode active material layer, for example, 65 wt% to 95 wt%, or 75 wt% to 91 wt%.

[0090] In addition, in the positive electrode active material layer, 65 wt% to 99 wt% of the positive electrode active material and 1 wt% to 35 wt% of the solid electrolyte may be included based on the total weight of the positive electrode active material and the solid electrolyte, for example, 80 wt% to 90 wt% of the positive electrode active material and 10 wt% to 20 wt% of the solid electrolyte may be included. When the solid electrolyte is included in the positive electrode in such an amount, the efficiency and life characteristics of the all-solid-state secondary battery can be improved without reducing the capacity.

[0091] The above positive electrode active material layer may further include a binder and / or a conductive material.

[0092] The above binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector, and representative examples thereof include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. In the positive electrode active material layer, the content of the binder may be approximately 0.1 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer.

[0093] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and is electronically conductive can be used. Examples of such conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof. The content of the conductive material in the positive electrode active material layer may be 0 wt% to 3 wt%, 0.01 wt% to 2 wt%, or 0.1 wt% to 1 wt% based on 100 wt% of the positive electrode active material layer.

[0094] All-solid-state secondary battery

[0095] In one embodiment, an all-solid-state secondary battery structure is provided, including the aforementioned positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and negative electrode.

[0096] Fig. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to Fig. 1, the all-solid-state secondary battery (100) has a structure in which an electrode assembly in which a negative electrode (400) including a negative electrode current collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode current collector (201) are laminated is housed in a battery case. The all-solid-state secondary battery (100) may further include an elastic sheet (500) on the outer side of at least one of the positive electrode (200) and the negative electrode (400). FIG. 1 illustrates an assembly in which two unit cells including a cathode (400), a solid electrolyte layer (300), and an anode (200) are laminated, but three or more may be laminated, for example, 2 to 100, 3 to 50, 4 to 20, etc.

[0097] cathode

[0098] An anode for an all-solid-state secondary battery includes a current collector and a negative electrode active material layer positioned on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0099] The above negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0100] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0101] As the above lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0102] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used, and the Si-based negative electrode active material may be silicon, a silicon-carbon composite, or SiO. x(0 < x < 2), Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn-based negative electrode active materials include Sn, SnO2, Sn-R alloy (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2 for use. The above elements Q and R may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0103] For example, the negative active material may include silicon-carbon composite particles. The average particle diameter (D50) of the silicon-carbon composite particles may be, for example, 0.5 μm to 20 μm. The average particle diameter (D50) is measured by a particle size analyzer and refers to the diameter of particles having a cumulative volume of 50% by volume in a particle size distribution. With respect to 100 wt% of the silicon-carbon composite particles, silicon may be included in an amount of 10 wt% to 60 wt% and carbon may be included in an amount of 40 wt% to 90 wt%. The silicon-carbon composite particles may include, for example, a core including silicon particles and a carbon coating layer positioned on a surface of the core. The average particle diameter (D50) of the silicon particles in the core may be, for example, 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 <x<2)로 표시될 수 있다. 또한, 상기 탄소 코팅층의 두께는 약 5 nm 내지 100 nm일 수 있다.

[0104] For example, the silicon-carbon composite particle may include a core including silicon particles and crystalline carbon, and a carbon coating layer located on the surface of the core and including amorphous carbon. For example, in the silicon-carbon composite particle, the amorphous carbon may not be present in the core but may be present only in the carbon coating layer. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof, and the amorphous carbon may be formed from coal pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, or a polymer resin (phenol resin, furan resin, polyimide resin, etc.). At this time, the content of the crystalline carbon may be 10 wt% to 70 wt%, and the content of the amorphous carbon may be 20 wt% to 40 wt% with respect to 100 wt% of the silicon-carbon composite particle.

[0105] In the above silicon-carbon composite particle, the core may include a void in the central portion. The radius of the void may be 30% to 50% of the radius of the silicon-carbon composite particle.

[0106] The silicon-carbon composite particles described above can effectively suppress problems such as volume expansion, structural collapse, or particle crushing due to charge and discharge, thereby preventing the phenomenon of conductive path disconnection, realizing high capacity and high efficiency, and are advantageous for use under high voltage or fast charging conditions.

[0107] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight.

[0108] The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative active material layer.

[0109] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. In addition, when the negative electrode active material layer further includes a conductive material, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0110] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

[0111] The above-mentioned non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0112] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0113] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity as a type of thickener may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li. The amount of the thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0114] The above conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and is electronically conductive can be used. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials including copper, nickel, aluminum, silver, etc. and in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0115] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0116] As another example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode. The precipitation-type negative electrode may refer to a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this acts as a negative electrode active material.

[0117] Fig. 2 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation-type negative electrode. Referring to Fig. 2, the precipitation-type negative electrode (400') may include a current collector (401) and a negative electrode coating layer (405) positioned on the current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material is present, and during charging, high-density lithium metal is precipitated or deposited between the current collector (401) and the negative electrode coating layer (405) or on the negative electrode coating layer (405) to form a lithium metal layer (404), which may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) positioned on the current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0118] The above cathode coating layer (405) may be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a metal, carbon material, or a combination thereof that acts as a catalyst.

[0119] The metal may be a lithium-philic metal, and may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one type of these or may be composed of several types of alloys. When the metal is present in the form of particles, the average particle diameter (D50) thereof may be about 4 μm or less, and may be, for example, 10 nm to 4 μm.

[0120] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

[0121] When the above-described negative electrode coating layer (405) includes both the metal and the carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The above-described negative electrode coating layer (405) may include, for example, a carbon material supported with a catalytic metal, or may include a mixture of metal particles and carbon material particles.

[0122] The above-described cathode coating layer (405) may include, for example, the above-described lithium-philic metal and amorphous carbon, in which case the precipitation of the lithium metal may be effectively promoted. As a specific example, the cathode coating layer (405) may include a composite in which a lithium-philic metal is supported on amorphous carbon.

[0123] The above cathode coating layer (405) may further include a binder, and the binder may be, for example, a conductive binder. In addition, the above cathode coating layer (405) may further include general additives such as fillers, dispersants, and ionic conductive agents.

[0124] The thickness of the cathode coating layer (405) may be, for example, 100 nm to 20 ㎛, or 500 nm to 10 ㎛, or 1 ㎛ to 5 ㎛.

[0125] The above-described precipitated negative electrode (400') may further include, for example, a thin film on the surface of the current collector, i.e., between the current collector and the negative electrode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one type thereof or may be composed of multiple types of alloys. The thin film may further flatten the precipitated form of the lithium metal layer (404) and further improve the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0126] The lithium metal layer (404) may include lithium metal or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

[0127] The thickness of the lithium metal layer (404) may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the lithium metal layer (404) is too thin, it may be difficult to perform the role of a lithium storage, and if it is too thick, the battery volume may increase and performance may deteriorate.

[0128] When such a precipitation-type cathode is applied, the cathode coating layer (405) can play a role in protecting the lithium metal layer (404) and suppressing the precipitation growth of lithium deadlight. Accordingly, short-circuiting and capacity reduction of the all-solid-state battery can be suppressed, and the life characteristics can be improved.

[0129] solid electrolyte layer

[0130] In an all-solid-state secondary battery according to one embodiment, the solid electrolyte layer (300) may include an inorganic solid electrolyte such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0131] Since the sulfide-based solid electrolyte has been described above, a detailed description will be omitted.

[0132] Oxide-based inorganic solid electrolytes include, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12(M= Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof.

[0133] Meanwhile, the average particle diameter (D50) of the solid electrolyte included in the solid electrolyte layer (300) may be larger than the average particle diameter (D50) of the solid electrolyte included in the positive electrode (200). In this case, the energy density of the all-solid-state secondary battery can be maximized while increasing the mobility of lithium ions, thereby improving the overall performance. For example, the average particle diameter (D50) of the solid electrolyte included in the positive electrode (200) may be 0.1 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D50) of the solid electrolyte included in the solid electrolyte layer (300) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized, while the transfer of lithium ions is facilitated, thereby suppressing resistance and improving the overall performance of the all-solid-state secondary battery.

[0134] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. The binder may include, for example, nitrile-butadiene rubber, hydrogenated nitrile-butadiene rubber, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluoroelastomer, polydimethylsiloxane, polyethylene oxide, polyvinylpyrrolidone, polyvinylpyridine, chlorosulfonated polyethylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene, ethylene propylene copolymer, ethylene propylene diene copolymer, polyamideimide, polyimide, poly(meth)acrylate, polyacrylonitrile, polystyrene, polyurethane, or a combination thereof.

[0135] The solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the same on a substrate film, and drying the same. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer formation process is widely known in the art, a detailed description thereof will be omitted.

[0136] The solid electrolyte layer (300) may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0137] The above alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt may improve ion conductivity by enhancing the lithium ion mobility of the solid electrolyte layer.

[0138] The lithium salts include, for example, LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, LiCl, LiF, LiBr, LiI, LiB(C2O4)2, LiBF4, LiBF3(C2F5), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LIODFB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoro methanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, It may include LiN(SO2F)2), LiCF3SO3, LiAsF6, LiSbF6, LiClO4 or mixtures thereof.

[0139] In addition, the lithium salt may be an imide-based one, and for example, the imide-based lithium salt may include lithium bis(trifluoro methanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2). The lithium salt may maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with an ionic liquid.

[0140] The above ionic liquid has a melting point below room temperature and is a salt or room-temperature molten salt that is liquid at room temperature and consists only of ions.

[0141] The above ionic liquid comprises a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof, and b) BF4. - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - It may be a compound containing one or more anions selected from among.

[0142] The ionic liquid may be at least one selected from the group consisting of, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0143] In the above solid electrolyte layer, the weight ratio of the solid electrolyte and the ionic liquid may be 0.1:99.9 to 90:10, for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying the above range can maintain or improve ionic conductivity by improving the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

[0144] The above-mentioned all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

[0145] The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state secondary battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage, and for example, it can be used in electric bicycles or power tools, etc. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0146] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0147] Example 1

[0148] 1. Manufacturing of the anode

[0149] A carbon coating layer composition was prepared by dispersing multilayer carbon nanotubes in an N-methyl-2-pyrrolidone solution containing 10 wt% polyvinylidene fluoride binder. This was applied to the surface of a 17 μm thick aluminum foil current collector and dried at 120°C for 4 hours, thereby forming a carbon coating layer with a thickness of approximately 1 to 20 nm on the current collector.

[0150] A dopamine buffer solution having a molar concentration of 0.001 to 0.05 M was prepared by mixing tris(hydroxymethyl)aminomethane and methoxyphenol in distilled water. A collector having a carbon coating layer formed thereon was immersed in the solution to induce a uniform polydopamine coating, which was then taken out and washed with distilled water, thereby producing a substrate having a polydopamine coating layer having a thickness of about 5 nm or less formed on the carbon coating layer.

[0151] Cathode active material coated with Li2O-ZrO2 (LiNi 0.8 Co 0.15 Mn 0.05 O2) 85 wt%, 13.5 wt% of an argyrodite-type solid electrolyte (Li6PS5Cl, D50=1.3㎛), 1.0 wt% of a polyvinylidene fluoride binder, and 0.5 wt% of a carbon nanotube conductive material were mixed to prepare a positive electrode composition. The prepared positive electrode composition was applied onto the polydopamine coating layer using a bar coater, and dried and rolled to prepare a positive electrode.

[0152] 2. Preparation of solid electrolyte layer

[0153] A solid electrolyte layer slurry was prepared by adding an argyrodite-type solid electrolyte Li6PS5Cl (D50=3㎛) to a binder solution in which an acrylic binder (SX-A334, Zeon) was dissolved in an isobutyryl isobutyrate solvent and stirring the solution. The slurry contained 98.5 wt% of the solid electrolyte and 1.5 wt% of the binder. The slurry was applied onto a release PET film using a bar coater and dried at room temperature to prepare a solid electrolyte layer.

[0154] 3. Manufacturing of the cathode

[0155] An Ag / C composite was prepared by mixing carbon black having a primary particle size of approximately 30 nm and silver (Ag) having an average particle size of approximately 60 nm in a weight ratio of 3:1, and 0.25 g of the composite was added to 2 g of an NMP solution containing 7 wt% polyvinylidene fluoride binder and mixed to prepare a negative electrode coating layer composition. This was applied to a nickel foil current collector using a bar coater and vacuum-dried, thereby preparing a deposition-type negative electrode in which a negative electrode coating layer was formed on the current collector.

[0156] 4. Manufacturing of all-solid-state batteries

[0157] An all-solid-state secondary battery was manufactured by laminating a cathode, a solid electrolyte layer, and an anode in that order, inserting an elastic sheet into the outermost layer, placing it in a laminate film, and pressing it with a warm isostatic press (WIP) at 80°C and 500 MPa for 30 minutes.

[0158] Comparative Example 1

[0159] A positive electrode was manufactured and an all-solid-state secondary battery was manufactured in substantially the same manner as in Example 1, except that a polydopamine coating layer was not formed.

[0160] Evaluation Example 1: Electrical Performance Evaluation

[0161] In order to compare the oxidation degree of the solid electrolyte, a substrate was prepared by sequentially forming a carbon coating layer and a polydopamine coating layer on an aluminum current collector as in Example 1, and then a solid electrolyte layer slurry was applied thereto and dried to form a solid electrolyte layer, and then lithium metal was laminated to manufacture a symmetrical cell of Example 1 having a Li / solid electrolyte layer / substrate configuration. Similarly, a substrate was prepared by forming only a carbon coating layer on an aluminum current collector as in Comparative Example 1, and then a solid electrolyte layer was formed and lithium metal was laminated to manufacture a symmetrical cell according to Comparative Example 1.

[0162] Cyclic voltammetry (CV) evaluation was performed on the symmetric cells of Example 1 and Comparative Example 1, and the results are shown in Fig. 3. Referring to Fig. 3, in the case of Comparative Example 1, oxidation of the solid electrolyte occurs at a voltage of 4.0 V or higher, whereas in the case of Example 1, oxidation of the solid electrolyte hardly occurs over the entire voltage range up to 4.5 V. Accordingly, it can be confirmed that the introduction of a polydopamine coating layer can effectively suppress the interfacial side reaction between the carbon coating layer of the substrate and the sulfide-based solid electrolyte.

[0163] Evaluation Example 2: Evaluation of the adhesive strength of the anode

[0164] In Example 1, a positive electrode composition was applied to a substrate, and the positive electrode in a dried state, and in Comparative Example 1, a positive electrode composition was applied to a substrate, and the dried positive electrode, were cut into test pieces of 25 mm x 100 mm in size. Using a peel strength measuring device, the 180° peel strength between the substrate and the positive electrode active material layer was measured at a peel speed of 100 mm / min and a measurement distance of 35 mm at a temperature of 25°C. Fig. 4 shows a graph of peel strength according to the measurement distance, and Fig. 5 shows the force required to peel 35 mm. The peel strength test was performed twice for each of Example 1 and Comparative Example 1, and is represented by A and B, respectively.

[0165] Referring to FIGS. 4 and 5, the anode peel strength of Comparative Example 1 was at the level of 0.33 to 0.35 gf / mm, whereas the anode peel strength of Example 1 was at the level of 0.50 to 0.51 gf / mm, confirming that the adhesion of the anode active material layer to the substrate was improved. In the Example, it is understood that by introducing a polydopamine layer to the anode substrate, the contact area between the substrate and the anode active material particles can be maximized, thereby increasing the adhesion and further reducing the electronic resistance of the interface.

[0166] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0167] [Explanation of symbols]

[0168] 100: All-solid-state battery 200: Cathode

[0169] 201: Cathode current collector 203: Cathode active material layer

[0170] 300: Solid electrolyte layer 400: Cathode

[0171] 401: Negative current collector 403: Negative active material layer

[0172] 400': Precipitation type cathode 404: Lithium metal layer

[0173] 405: Cathode coating layer 500: Elastic layer

Claims

1. The entire house, A carbon coating layer positioned on the above collector, A polydopamine coating layer positioned on the carbon coating layer, and A positive electrode for an all-solid-state secondary battery comprising a positive electrode active material layer positioned on the polydopamine coating layer and containing a positive electrode active material and a sulfide-based solid electrolyte.

2. In paragraph 1, The above-mentioned positive electrode for an all-solid-state secondary battery comprises aluminum, nickel, stainless steel, or a combination thereof.

3. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the thickness of the carbon coating layer is 1 nm to 50 nm.

4. In paragraph 1, The above carbon coating layer is an all-solid-state secondary battery positive electrode including natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, or a combination thereof.

5. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the thickness of the polydopamine coating layer is 1 nm to 20 nm.

6. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the thickness of the polydopamine coating layer is 5 nm or less.

7. In paragraph 1, The above sulfide-based solid electrolyte is a positive electrode for an all-solid-state secondary battery containing an argyrodite-type sulfide.

8. In paragraph 7, The above argyrodite-type sulfides are Li3PS4, Li7P3S 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 Or a cathode for an all-solid-state secondary battery which is a combination of these.

9. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the above sulfide-based solid electrolyte is in the form of particles and the average particle diameter (D50) of the particles is 0.1 ㎛ to 1.9 ㎛.

10. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the positive electrode active material comprises a lithium transition metal composite oxide and is in the form of particles, and the average particle diameter (D50) of the particles is 1 ㎛ to 25 ㎛.

11. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the positive electrode active material is included in an amount of 65 to 99 wt% and the sulfide-based solid electrolyte is included in an amount of 1 to 35 wt%, based on 100 wt% of the total of the positive electrode active material and the sulfide-based solid electrolyte in the positive electrode active material layer.

12. In paragraph 1, A positive electrode for an all-solid-state secondary battery, wherein the thickness of the positive electrode active material layer is 20 ㎛ to 200 ㎛.

13. The anode according to any one of paragraphs 1 to 12; cathode, and An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive and negative electrodes.

14. In paragraph 13, The negative electrode comprises a current collector and a negative electrode coating layer positioned on the current collector and containing a lithium-philic metal, a carbon material, or a combination thereof, An all-solid-state secondary battery comprising a lithium metal layer formed by charging between the above-described current collector and the negative electrode coating layer.

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